Forsmark is best known today for its nuclear power station, but the older draw is Forsmark Bruk, one of the ironworking estates that made northern Uppland important in Sweden's early modern economy. The setting is orderly and green, with manor buildings, water, and the remains of an industrial village.
It is a good stop if you are tracing the Walloon ironworks of Roslagen. The contrast between the old bruk and the modern power plant nearby is also very Swedish: history, engineering, and landscape sitting side by side without much drama.